1. Field of the Invention
This invention relates to the sealing together of the peripheral portions of two flexible sheets.
2. Description of the Prior Art
Sealing together of two flexible sheets is required, for example, in the forming of airtight containers using flexible covers. Such containers are used for the storage of goods; the use of a flexible cover is particularly advantageous if the container is partially evacuated of air so that the flexible sheet or sheets collapse around the goods in the container thereby holding them securely in place. As an example of such a container, reference may be made to U.S. Pat. No. 3,929,178. Heretofore however, the sealing together of two sheets to form an airtight seal has required either continuous welding along the length of the seal or the provision of a rigid sealing system. Continuous welding is not wholly reliable because any gap in the welding will cause an air leak. For that reason, it has heretofore been preferred to effect sealing by putting the peripheries of the two sheets together in a slot or groove formed in a rigid member extending around the periphery. A tight seal can be obtained then by inflating a flexible tube in the slot or groove to force the peripheral portions of the sheets into tight contact. Such an arrangement is disclosed for example in the aforementioned U.S. Pat. No. 3,929,178. It results however in a rigid structure of predetermined dimensions irrespective of the size of the goods within the container.